Crystal structure, morphotropic phase transition and luminescence in the new cyclosilicates Sr3R2(Si3O9)2, R=Y, Eu–Lu

Rb2Ln[Si2O6]F (Ln = Y, Eu-Lu): Flux Synthesis, Structure Determination, and DFT-Calculated Formation Enthalpies of a Series of Mixed-Anion Rare Earth Cyclosilicates

A new series of mixed-anion alkali rare earth silicate fluorides with composition Rb2Ln[Si2O6]F (Ln = Y, Eu-Lu) has been synthesized via an alkali chloride/fluoride eutectic flux synthetic route. All synthesized compositions crystallize in the tetragonal space group P42/mnm with a 3D framework consisting of LnO4F2 octahedra, tetrasilicate rings, and 1D channels containing alkali metals. A combination of powder X-ray diffraction, single-crystal X-ray diffraction, and luminescence emission spectroscopy was performed to characterize the reaction products. In addition, density functional theory (DFT) calculations were utilized to calculate the 0 K formation enthalpies of the synthesized phases and of hypothetical trivalent actinide analogues to probe the likelihood of the successful synthesis of such trivalent transuranic containing phases, specifically Am and Cm, in the future.

Structural and spectroscopic characterization of a new series of Ba2RE2Ge4O13 (RE = Pr, Nd, Gd, and Dy) and Ba2Gd2-xEuxGe4O13 tetragermanates

A new series of Ba₂RE₂Ge₄O₁₃ (RE = Pr, Nd, Gd, Dy) germanates and Ba₂Gd_2-xEu_xGe₄O₁₃ (x = 0.1-0.8) solid solutions have been synthesized using the solid-state reaction technique and characterized by X-ray powder diffraction. All compounds crystallize in the monoclinic system, space group C2/c, Z = 4. The crystal lattice consists of RE₂O₁₂ dimers, zigzag C₂-symmetric [Ge₄O₁₃]^10- tetramers, and ten-coordinated Ba atoms located in voids between polyhedra. The density-functional theory (DFT) calculations performed on a rich set of Ba₂RE₂Ge₄O₁₃ compounds have confirmed the high thermodynamic stability of monoclinic modification. Under ultraviolet (UV) light excitation Ba₂Gd_2-xEu_xGe₄O₁₃ phosphors exhibit an orange-red emission corresponding to the characteristic f-f transitions in Eu³⁺ ions. The highest intensity of lines at 580 nm (⁵D₀→⁷F₀), 582-602 nm (⁵D₀→⁷F₁), 602-640 nm (⁵D₀→⁷F₂), 648-660 nm (⁵D₀→⁷F₃), and 680-715 nm (⁵D₀→⁷F₄) is observed for the samples with x = 0.4-0.6. The possibility of their application has been assessed by studying their color characteristics, quantum efficiency, and thermal stability. The obtained data indicate that Ba₂Gd_2-xEu_xGe₄O₁₃ solids can be considered as promising materials for UV-excited phosphor-converted light-emitting diodes (LEDs) if an aluminum nitride substrate (λ_ex = 255 nm) is used as a semiconductor chip.

Gd3+-activated narrowband ultraviolet-B persistent luminescence through persistent energy transfer

This work reports the realization of Gd3+ persistent luminescence in the narrowband ultraviolet-B (NB-UVB; 310-313 nm) through persistent energy transfer from a sensitizer of Pr3+, Pb2+ or Bi3+. We propose a general design concept to develop Gd3+-activated NB-UVB persistent phosphors from Pr3+-, Pb2+- or Bi3+-activated ultraviolet-C (200-280 nm) or ultraviolet-B (280-315 nm) persistent phosphors, leading to the discovery of ten Gd3+ NB-UVB persistent phosphors such as Sr3Gd2Si6O18:Pr3+, Sr3Gd2Si6O18:Pb2+ and Y2GdAl2Ga3O12:Bi3+ as well as five ultraviolet-B persistent phosphors such as Y3Al2Ga3O12:Pr3+, Sr3Y2Si6O18:Pb2+ and Y3Al2Ga3O12:Bi3+. The persistent energy transfer from the sensitizers to Gd3+ is very efficient and the Gd3+ NB-UVB afterglow can last for more than 10 hours. This study expands the persistent luminescence research to the NB-UVB as well as the broader ultraviolet-B spectral regions. The NB-UVB persistent phosphors may act as self-sustained glowing NB-UVB radiation sources for dermatological therapy.

Solar-blind ultraviolet-C persistent luminescence phosphors

Visible-light and infrared-light persistent phosphors are extensively studied and are being used as self-sustained glowing tags in darkness. In contrast, persistent phosphors for higher-energy, solar-blind ultraviolet-C wavelengths (200-280 nm) are lacking. Also, persistent tags working in bright environments are not available. Here we report five types of Pr3+-doped silicates (melilite, cyclosilicate, silicate garnet, oxyorthosilicate, and orthosilicate) ultraviolet-C persistent phosphors that can act as self-sustained glowing tags in bright environments. These ultraviolet-C persistent phosphors can be effectively charged by a standard 254 nm lamp and emit intense, long-lasting afterglow at 265-270 nm, which can be clearly monitored and imaged by a corona camera in daylight and room light. Besides thermal-stimulation, in bright environments, photo-stimulation also contributes to the afterglow emission and its contribution can be dominant when ambient light is strong. This study expands persistent luminescence research to the ultraviolet-C wavelengths and brings persistent luminescence applications to light.

Structure, magnetic and optical properties of Sr3RE2(Ge3O9)2 cyclogermanates (RE = La–Gd)

A new group of cyclogermanates has been characterized using XRD, DFT calculations, photoluminescence spectroscopy and magnetic study.

A strategy for realizing tunable luminescence and full-color emission in Sr3Gd2(Si3O9)2:Eu phosphors by introducing dual functional Mn2+

The introduced Mn²⁺ ion can act as both an activator and a structure regulator in the SGSO:Eu system to achieve full-color emission and tunable luminescence of SGSO:0.03Eu,Mn phosphors.

Structural evolution induced preferential occupancy of designated cation sites by Eu2+ in M5(Si3O9)2 (M = Sr, Ba, Y, Mn) phosphors

A schematic presentation for the unexpected blue-shifted luminescence of Eu²⁺ in M₅(Si₃O₉)₂ (M = Sr, Ba, Y, Eu, Mn) based on the preferential occupancy at the designated cation sites.

Structure, luminescence properties and energy transfer behavior of color-adjustable Sr3Gd2(Si3O9)2:Ce3+, Tb3+/Mn2+ phosphors

A series of SGSO:Ce³⁺, Tb³⁺/Mn²⁺ phosphors were synthesized via a solid-state reaction. The emission colors can modulate from blue to green and near white due to energy transfer from Ce³⁺ to Tb³⁺ or Mn²⁺, which can serve as UV-convertible phosphors.

Synthesis and structural study of a new group of trigermanates, CaRE2Ge3O10(RE = La–Yb)

The changes in the Ge₃O₁₀conformation and coordination environment of the three nonequivalent sites of metal cations within the structures of CaY₂Ge₃O₁₀, CaPr₂Ge₃O₁₀and CaLa₂Ge₃O₁₀.